Electric and hybrid vehicle propulsion systems typically employ an alternating current (AC) driving circuit, such as an inverter, to convert direct current (DC) voltage of an energy storage battery to variable speed AC waveforms to drive an electric motor. The driving circuit often has a current controlled voltage source configuration. Power electronic devices such as insulated gate bipolar transistors (IGBTs) can be used as switches to construct AC voltages for driving the electric motor by chopping the DC voltage according to a pulse width modulation (PWM) scheme.
The torque output of an electric motor is roughly proportional to the current applied to the electric motor. Therefore, in order to obtain a high torque, a large amount of current needs to be applied to the electric motor by the driving circuit. On the other hand, overcurrent should be monitored to prevent damaging the power electronic devices of the driving circuit. Thus, it is desirable to develop a driving circuit to provide high current output and at the same time to accurately monitor overcurrent conditions.